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George's Service Remedial Action Work Plan Project No.425.2 June 30,2011 In addition, pump and treat may not be effective at this site for the following reasons: • The length of time a pump and treat system would require to achieve remediation, • The large volumes of groundwater needed to be extracted for a pump and treat system to be effective to extract dissolved-phase hydrocarbons and/or achieve hydraulic control to prevent offsite migration • No capability for Source Area removal within the unsaturated zone, • The possibility of renewed groundwater impact subsequent to system shutdown, and, • The likelihood that treated discharge from a pomp and treat system would be flow- restricted by disposal options. 5.3. In Situ Chemical Oxidization The process of in slat chemical oxidation has been used successfully in many applications. Advanced Oxidation Processes (AOPs) are processes that create and use a highly reactive radical that effectively oxidizes organic compounds by chemical reaction. The most prominently used radical is the hydroxyl radical, designated as OH. The OH ion will capture a hydrogen atom from a molecule of contaminant, which then causes the contaminant molecule to become unstable and breakdown. The AOPs have been very successful at treating gasoline compounds and the gasoline oxygenated fuel compounds. AOPs are promising because they quickly destroy the contaminant rather than just augmenting the relatively slow biological processes at the site. It is noted that a byproduct of injecting oxidizing agents is an increase in the oxygen content of the subsurface to promote biodegradation rates. The basic chemistry of reduction-oxidation (Redox) reactions is a combination of chemical reactions (changes in chemical bonding) and the transfer of electrons. A more detailed explanation is: specific bonds are broken while others are formed when a donor gives up an electron (e) and a receptor acquires the e-. In the case of petroleum contamination, BTEX and TPH-G are reduced (gain of electrons and a decrease in valence) and in an aerobic environment oxygen is oxidized (loss of electrons and increase in valence). In an anaerobic environment, oxygen has been depleted by this reaction and mineral compounds, such as Mn02, NO3, Fe(0)3, SO4 and H+, become the a donor(listed in decreasing Eh values). The half-life of ozone in the presence of water is typically 30 minutes at standard temperatures and pressures, but it can be longer in subsurface environments. Depending on the concentrations of contaminants present in the subsurface, delivery may need to be sustained over a longer period of time than the other oxidants. The contaminants are treated in situ, converted to innocuous and/or natural occurring compounds [e.g. H2O, CO2, and 02 halide ions]. Because ozone is a gas, it can easily be used to remediate vadose zone contamination. As a side benefit, ozone provides oxygen to the microbial community, as it decomposes, which can aid in bioremediation. otological Technics/a. 9 4252 RAP.docx